Original Workaround

First off I want to clarify that I have the same issue and so I want to give some further details on the hardware (for all those who might be able to debug the error):

HP Spectre x360 15-bl002ng

Intel i7-7500U

Nvidia 940MX

NVME PCIe SSD (Samsung I believe)

Second:

I found a workaround by setting the systemd timeout to 10s instead of 90s. To do so, edit /etc/systemd/system.conf. In my case I had to uncomment the following two lines set the timer:

DefaultTimeoutStartSec=10s
DefaultTimeoutStopSec=10s

After a reboot, the system is up after about 10 seconds. May be warned however, that such a low timeout may cause other, more severe problems. So do that at your own risk!

Third:

For all those who can actually figure out what might be wrong I would like to add what I found out:

After I upgraded to kernel 4.11 RC8 (to fix intel-vbtn INT33D6:00: unknown event index 0xcd, comment #24) I got way more debug info and so noticed that the boot sequence is actually stuck at A start job is running for [some dev + UUID presumably].

I stumbled across a German Debian forum where the error seems to be caused by a mismatch of the actually UUID of the swap partition reported by sudo blkid and the used UUID by fstab.

However, since 17.04 Ubuntu uses a swapfile instead of a partition, I am clueless on how to fix this issue.